KVM: Do not take reference to mm during async #PF (62c49cc9) · Commits · 戴 / test

It turned to be totally unneeded. The reason the code was introduced is so that KVM can prefault swapped in page, but prefault can fail even if mm is pinned since page table can change anyway. KVM handles this situation correctly though and does not inject spurious page faults. Fixes: "INFO: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected" warning while running LTP inside a KVM guest using the recent -next kernel. Reported-by:

Sasha Levin <levinsasha928@gmail.com> Signed-off-by:

Gleb Natapov <gleb@redhat.com> Signed-off-by:

Avi Kivity <avi@redhat.com>

arch/x86/kernel/kvm.c

+1 −8

Original line number	Diff line number	Diff line
		@@ -79,7 +79,6 @@ struct kvm_task_sleep_node {
		u32 token;
		int cpu;
		bool halted;
		struct mm_struct *mm;
		};

		static struct kvm_task_sleep_head {
		@@ -126,9 +125,7 @@ void kvm_async_pf_task_wait(u32 token)

		n.token = token;
		n.cpu = smp_processor_id();
		n.mm = current->active_mm;
		n.halted = idle \|\| preempt_count() > 1;
		atomic_inc(&n.mm->mm_count);
		init_waitqueue_head(&n.wq);
		hlist_add_head(&n.link, &b->list);
		spin_unlock(&b->lock);
		@@ -161,9 +158,6 @@ EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait);
		static void apf_task_wake_one(struct kvm_task_sleep_node *n)
		{
		hlist_del_init(&n->link);
		if (!n->mm)
		return;
		mmdrop(n->mm);
		if (n->halted)
		smp_send_reschedule(n->cpu);
		else if (waitqueue_active(&n->wq))
		@@ -207,7 +201,7 @@ again:
		* async PF was not yet handled.
		* Add dummy entry for the token.
		*/
		n = kmalloc(sizeof(*n), GFP_ATOMIC);
		n = kzalloc(sizeof(*n), GFP_ATOMIC);
		if (!n) {
		/*
		* Allocation failed! Busy wait while other cpu
		@@ -219,7 +213,6 @@ again:
		}
		n->token = token;
		n->cpu = smp_processor_id();
		n->mm = NULL;
		init_waitqueue_head(&n->wq);
		hlist_add_head(&n->link, &b->list);
		} else

Admin message